Performance Study of a Solar Tunnel Dryer for Horticultural Crops

Abstract

Performance of a solar tunnnel dryer developed at Central Institute of Agricultural Engineering, Bhopal was studied under no-load and for drying unripe peeled mango. It is a batch type dryer (80 to 90 Kg wet product/batch), of modular construction to facilitate transport, installation and capacity enchancement. Solar air heaters are directly connected to the drying tunnel to reduce the cost. The dryer is 2.0 m wide, with a 4.5 m solar air heater and a drying tunnel of 8.0 m. The heater and dryer are covered with UV stabilized polyethylene film. The total collector area of the dryer is 25 sq m. Solar photo-voltaic (SPV) operated axial flow fans have been provided at one end of push fresh air in to the dryer. An exhaust fan is provided at the other end to evacuate hot air and to control the air temperature, with the help of an electronic temperature controller automatically. Air temperature inside the dryer could be maintained in the range of 50 to 75?C on typical sunny days. Cut mango pieces were uniformly spread over the drying trays at the rate of 4.5 kg/m2. Initial moisture content of mango was around 79%. The mango pieces could be dried in the solar dryer in four and a half days to a moisture level of 4.2% as compared to ten days in the open drying to a moisture content of 4.7%. The average drying temperature in the tunnel was 60?C. Quality of the product dried in the tunnel dryer was found to be superior the sun-dried product in terms fo microbial load, appearance and acceptability.